# User manual | METHODICAL INSTRUCTIONS for laboratory lesson

МІНІСТЕРСТВО ТРАНСПОРТУ ТА ЗВЯЗКУ УКРАЇНИ

ДЕРЖАВНИЙ ДЕПАРТАМЕНТ З ПИТАНЬ ЗВЯЗКУ ТА ІНФОРМАТИЗАЦІЇ

ОДЕСЬКА НАЦІОНАЛЬНА АКАДЕМІЯ ЗВ'ЯЗКУ ім. О.С. ПОПОВА

Кафедра комутаційних систем

М Е Т О Д И Ч Н І В К А З І В К И до виконання лабораторної роботи 11

ТЕЛЕФОННІ АПАРАТИ з курсу «Системи комутації в електрозвязку»

M E T H O D I C A L I N S T R U C T I O N S for laboratory lesson

11

“TELEPHONE SETS” within the course of telecomminication switching systems

## Odessa 2008

2

Укладачі: Ложковський А.Г., Бабіч Ю.О.

## CONTENTS

Laboratory lesson № 11

TELEPHONE SETS …………………………………………………………… 3

Laboratory lesson № 17

CROSSBAR EXCHANGE OF LOW CAPACITY …………………………… 13

Laboratory lesson № 18

QUASIELECTRONIC EXCHANGE OF LOW CAPACITY ………………… 27

## 1 Learning objectives

a) Learn the structure and operation principles of the simple telephone circuit b) Assemble the circuit of a telephone c) Research the assembled circuit

## 2 Theory

2.1 Subscriber terminal for telephone network is a telephone set that able to: a) generate connection requests; b) send address information; c) ring and accept the ringing tone; d) handle a call within the range of 0,3…3,4 kHz.

A schematic diagram of the telephone set (TS) is shown in the figure 1. The circuit contains:

ringing units;

voice units (the microphone – M and the speaker – S).

3

Figure 1 – Simplified schematic diagram of the TS

2.2 The cradle switch (CS) is intended either for connecting the ringing units to the line (if the handset is on the phone) or for connecting the voice units to the line

(if the handset is not on the phone).

2.3 The ringing units are intended for ringing. Polarized magneto bell is the most common example of the ringing units. It requires alternating current of 90 – 100

V and frequency of 25 Hz.

4

Modern phones use the tone ringers. They generate more pleasant sound of required loudness and frequency. They do not have any electromechanical components.

2.4 The dial pulser is intended for forming the pulses of address information

(the number of required subscriber). There are two manufactured types of the dial pulsers: a) disk dial pulsers; b) keytone senders.

The disk dial pulser has pulse springs (PS) and shunt springs (SS).

The pulse springs (1-2) (shown in the figure 1) break and close a loop of subscriber line in order to create series of pulses of direct current. Number of pulses

(breaks of the loop) encodes the dialed digit.

The rate of sending the pulses (f) must be 10 pulses per second. Pulse ratio looks like:

K t b

=

t c

=

1 , 4 ...

1 , 8 .

1

It is known that period of pulses

T

= =

t b

+

t c

. It is possible to calculate the

f

values of t

b

and t

c

if K and T are known. The shunt springs (4-3) are closed when you move the disc. They exclude reactive elements of TS circuit. Otherwise these elements can affect the pulses. The closure of shunt springs prevents a subscriber from hearing the pulses of pulse springs.

The keytone senders are capable of sending information in the decade code of loop pulses as well as the disk dial pulsers. The keytone senders have microchip and random access memory. Information about the phone with keytone sender can be found in the appendix.

Electronic TSs with the keytone senders can transmit address information encoded in the DTMF code.

2.5 The voice units are intended for receiving and sending voice. The voice units include: a) the microphone – M; b) the speaker – S; c) the transformer – T; d) the compromise network – CN.

The microphone converts sound oscillations to electrical oscillations. Carbon powder microphones are the most common due to their simplicity, cheapness and sufficient power (don’t require any amplification).

The carbon powder microphone is shown in the figure 2. The diaphragm is motionless if no sound oscillations hit it. I

0

direct current flows through the microphone from the source U (the source of constant voltage). During a conversation sound oscillations hit the diaphragm which changes the powder’s density. If the density of powder changes, its resistance changes too. The I

0

direct current is modulated by the current of voice frequency i

which creates variable magnetic flux through the transformer’s core. It results in induction of the appropriate

EMF at the second winding of the transformer.

It is possible to classify two types of microphones according to their resistance and required feed current.

5

Figure 2 – Simplified diagram of the carbon powder microphone

Table 1 – Parameters of the carbon powder microphones

Type of microphone

R

, Ohm

I

0

, mA Application

Middle-ohmic (MO) 65 – 145 25 – 60

l sl

< 6 km

High-ohmic (HO) 145 – 300 12 – 25

l sl

> 6 km

The speaker (S) converts electrical oscillations to sound oscillations. Common telephone sets use the electromagnetic speakers based on interaction of magnetic fluxes of a permanent magnet and electromagnet. The simplified diagram of the electromagnetic speaker is given in the figure 3.

Figure 3 – Simplified diagram of the electromagnetic speaker

Magnetic flux generated by the permanent magnet (F

) cases initial attraction force of the diaphragm. The polar tie-backs are made of magnetic material. They are required for obtaining the optimum value of magnetic flux through the diaphragm. It ensures minimal nonlinear distortions and loses on hysteresis. Absence of the

6 permanent magnet would have caused nonlinear distortions resulting in the diaphragm’s oscillations with doubled frequency [1].

Variable voltage of the voice frequency U

≈ comes to the windings of electromagnet’s coils. Depending on the current direction (going through the windings) variable magnetic flux increases or decreases initial attraction force of the diaphragm. As a result the diaphragm oscillates with appropriate amplitude which causes sound waves (P

).

The transformer (T) separates the microphone’s feeding circuit from the circuit of alternating current. The transformer and the compromise network (CN) create the antisidetone circuit together.

Sidetone effect takes place when you hear your voice from your hand set. The effect reduces distance and quality of voice transmission because signals coming from a line are masked by own voice of quite high level. This is why it is necessary to take measures to cope with the sidetone effect. Compromise networks of the bridge type are the most common nowadays. The simplified bridge circuit of a TS is shown in the figure 4 (a). a

(a) b

(b)

Figure 4 – Simplified diagram of the TS of the bridge type (a) and compromise type (b)

7

The diagram has the following arbitrary signs.

M – the microphone in kind of the generator at the bridge’s diagonal.

S – the speaker as a receiver at another diagonal with inductive connection.

Z

L

– resistance of a line.

Z

CN

– resistance of the compromise network.

Z

1

and Z

2

– resistances of the transformer’s windings.

The bridge is balanced if:

Z

1

·Z

CN

= Z

2

·Z

L

.

Meanwhile the current of the microphone (the generator at one of the bridge’s diagonals) divides into i

CN

and i

L

. In the ideal case there will be no current through the speaker (inductively connected to the second diagonal) circuit.

It is almost impossible in real life because TSs are connected to lines of a different length. Moreover it is possible to balance the bridge for the definite frequency only.

A capacitor C presents at the compromise network as well as R due to the capacitive nature of Z

L

.

Simplified diagram of the TS’s antisidetone circuit of the compromise type is shown in the figure 4 (b). The speaker circuit has magnetic and electric connection with line winding (W

L

) and compromise winding (W

C

) of the transformer (T). The

EMF is inducted at the W

S

winding during a conversation due to the difference between i

L

and i

C

currents. If the EMF (at the a and b points) is equal in value and opposite in phase to the i comp

·Z

C

voltage drop than there is no current through the speaker. The C capacitor prevents direct current flow through the speaker and reflects the capacitive nature of line’s resistance.

Check [1, Chapter 1] for more detailed diagrams of common telephone sets.

## 3 Test questions

3.1 Name all the units of the TS. Name all their functions and parameters.

3.2 Name all signals transmitted and received by the TS.

3.3 There is a capacitor switched in parallel with a bell. Why?

3.4 Tell the functions of all springs of the dial pulser.

3.5 Tell the value of feeding direct current for the carbon powder microphone.

3.6 The permanent magnet is required for the electromagnetic speaker. Why? they?

3.8 The TSs circuits use some ways to cope with sidetone effect. What are

3.9 The circuit of compromise networks has resistors and capacitors. Why?

8

learn:

4.1 Use the book [1, page 16] and Chapter 2 of the methodical instructions to

– the simplified schematic diagram of the TS and its main units;

– how the dial pulser works [1, p. 37, 38];

– the M and S and their operation principles [1, p. 20…23, 28…31];

4.2 Use the TS’s diagram to draw:

– the circuit of current flow when subscriber takes his handset off the phone;

the circuit of call receiving;

the circuit of dialing pulses transmission [use 1, figure 5.19 and 5.21 for it].

4.3 Calculate minimal and maximal values of feeding current for the microphone required for the following conditions. The TS with the middle-ohmic microphone is connected to the two windings of a feeding relay (500 Ω each winding) of a telephone exchange. Resistance of a subscriber line ranges from 0 to

1000 Ω. Voltage of a power source is 60 V.

4.4 Calculate break time t

b

and closure time t

c

for pulse springs of the dial pulser. Take the period T = 85 + 3X ms and pulse ratio K = 1,35 + 0,005Y. (where X is a number of your team in your subgroup and Y is a student’s number in the team).

## 5 Research plan

5.1 Familiarize yourself with the TS. Determine the types of the microphone and speaker. Familiarize yourself with the cradle switch, magneto bell, transformer and compromise network. Find how to change ring volume.

5.2 Familiarize yourself with the disk dial pulser. Find its pulse springs and shunt springs.

Connect the circuit of the TS (shown in the left bottom part of 4-th panel of a laboratory stand) to the windings of a pulse relay (its circuit is shown more to the right). Connect 60 V to other ends of the windings. Switch the power on and watch the indication lamps. They show current flow through the circuit. Slowly wind the disk of the dial pulser and watch how current flow changes (with the help of the indication lamps). Release the disk and watch the A relay operation (it receives pulse series) and indication on the panel.

5.3 Draw the chart based on the results of 5.2. The chart should depict how the states of pulse springs and shunt spring change when you wind the disk and when it moves back for dialing the X digit.

5.4 Familiarize yourself with laboratory equipment (check Chapter 6).

5.5 Assemble the circuit of the TS with the help of separate units on the panel

5. Check whether your circuit works.

– Use assembled circuit to call another subscriber (№ 3-33).

Check whether your circuit can accept calls.

Talk to another subscriber.

5.6 Measure the value of feeding current for the microphone of the assembled

TS. Compare measured value of the current to calculated (4.3) value.

9

## 6 Laboratory equipment

6.1 You can find the TS’s units on the 5-th panel of the laboratory stand. Line

(L1 and L2) is connected to the telephone exchange. The line has a number consisting of three digits. The number is written at the top of the panel 5. Laboratory equipment of every stand includes TS that can be connected to the stand and several TSs and dial pulser allowing to learn their constructions.

6.2 The feeding current for the microphone must be measured with an ammeter. It can be found on the panel 6. Connect one wire from the microphone to the ammeter in order to measure the feeding current. You should not do any measures unless voice connection is established.

## 7 Report contents

7.1 Simplified schematic diagram of the TS.

7.2 Three circuits according 4.2.

7.3 Calculations of currents according to 4.3. Calculations of break time t

b

and closure time t

c

according to 4.4.

7.4 Measure results according to 5.6.

10

## Construction features of an electronic telephone set manufactured by the domestic manufacturer. It is capable of sending information in the decade code of loop pulses.

Figure A1 – Simplified block diagram of the electronic telephone set

The main units of the TS are the following.

The ringing device (RD) accepts ringing signal of 25 Hz and converts it to a ring tone.

The dial pulser chip (DP chip) is a chip with random access memory of

CMOS technology.

The feeding circuit ensures feeding for the dial pulser chip during dialing and it feeds random access memory when the handset is on the phone.

The “on-hook” circuit resets the dial pulser chip.

The keypad is intended for dialing.

The antisidetone circuit (ASC) prevent the sidetone effect.

The microphone (M).

The speaker (S).

The electronic pulse contact (PC).

The voice contact (VC) exclude the voice units of the circuit during pulses sending period.

The diode bridge is not shown in the figure A1. It ensures correct operation of the TS’s units regardless of polarity at the wires (L1 and L2) of a line.

11

Taking the handset off the phone changes the position of CS. An amplifiers of the microphone and speaker receives power then.

The I

0

current flows through the TS.

i t b t c

I l

I

0

1

2 3

I

0 t,

ms

Handset is on the phone

Handset is off the phone

Button 3 is pressed. The VC is disconnected

End of dialing

Figure A2 – Time chart of dialing the digit 3.

The feeding circuit converts voltage of 60 V to 5 V and with the help of the

“on-hook” circuit resets the dial pulser chip. Meanwhile the pulse contact (PC) is disconnected and the VC is closed.

Pressing any button of the keypad results in sending pulses. At the same time the VC disconnects (excluding the voice units) and the pulse contact closes the wires

(L1 and L2) of the line. Quantity of breaks of subscriber loop encodes the dialed digit

(Dialing of the digit 3 is shown in the figure A2).

The current through the subscriber loop (I

l

) raises a little due to exclusion of voice units.

The circuit resets to initial state after dialing. If subscriber presses buttons to fast then number will be stored in RAM and transmitted with intertrain pause of

t ip

= 600 ms.

## Reference

1 Автоматические системы коммутации / О.Н. Иванова, М.Ф. Копп,

З.Г. Коханова, Г.Б. Метельский; под ред. О.Н. Ивановой. – М.: Связь, 1978.

12

## VOCABULARY FOR THE LABORATORY LESSON

11

Alternating current – змінний струм

Ammeter – амперметр

Antisidetone circuit – противомісцева схема

Attraction force – сила притягнення

Block diagram – структурна схема

Break and close – розмикання та замикання

Channel – канал

Capacitor – конденсатор

Circuit – схема

Carbon powder microphone – вугільний мікрофон

Coil – катушка

Compromise network – балансний контур

Connection request – запит на з’єднання (виклик абонентом станції)

Decade code of loop pulses – декадний код шлейфні імпульси

Density – щільність

Dial pulser – номеронабирач

Disk dial pulsers – дисковий номеронабирач

Direct current – постійний струм

EMF – ЕРС (електрорушійна сила)

High-ohmic – високоомний

Keytone senders – кнопковий номеронабирач

Laboratory stand – лабораторний стенд

LED indicator – світлодіодний індикатор

Loop of subscriber line – шлейф абонентської лінії

Middle-ohmic – середньоомний

Nonlinear distortions – нелінійні спотворення

Polarized magneto bell – поляризований дзвоник змінного струму

Polar tie-backs – полюсні надставки

Pulse ratio – імпульсний коефіцієнт

Pulse springs – імпульсні контакти

Ringing tone – сигнал КПВ

Ringing units – викличні прилади

Series of pulses – серії імпульсів

Sidetone effect – місцевий ефект

Schematic diagram – принципова схема

Shunt springs – шунтучі контакти

Telephone exchange – телефонна станція

Tone ringer – пристрій тонального виклику

Transformer – трансформатор

Transformer’s core – сердечник трансформатора

Variable magnetic flux – змінний магнітний потік

Voice units – розмовні прилади

Winding – обмотка

МІНІСТЕРСТВО ТРАНСПОРТУ ТА ЗВЯЗКУ УКРАЇНИ

ДЕРЖАВНИЙ ДЕПАРТАМЕНТ З ПИТАНЬ ЗВЯЗКУ ТА ІНФОРМАТИЗАЦІЇ

ОДЕСЬКА НАЦІОНАЛЬНА АКАДЕМІЯ ЗВ'ЯЗКУ ім. О.С. ПОПОВА

13

Кафедра комутаційних систем

М Е Т О Д И Ч Н І В К А З І В К И до виконання лабораторної роботи 17

КООРДИНАТНА АТС МАЛОЇ ЄМНОСТІ з курсу «Системи комутації в електрозвязку»

M E T H O D I C A L I N S T R U C T I O N S for laboratory lesson

17

“CROSSBAR EXCHANGE OF LOW CAPACITY” within the course of telecomminication switching systems

## Odessa 2008

14

Укладачі: Ложковський А.Г., Бабіч Ю.О.

15

## 1 Learning objectives

a) Learn the structure and operation principles of crossbar exchange of low capacity. b) Familiarize yourself with some electric circuits of analog telephone exchange (TE).

## 2 Theory

The crossbar TE has the following equipment (shown in the figure 1).

(a)

(b)

Figure 1 – Diagram of the crossbar TE of low capacity

It contains: a) ten customer units (CU); b) two cord circuits (CC);

16 c) the stage of subscriber selection (based on the 5×10×6 crossbar selector); d) the register (R)(it receives and stores a dialed number); e) the controller.

It is seen from the figure 1 that subscriber line is connected to the CU while the paralleled contacts of the fields of all the verticals of the crossbar selector (at the subscriber selection stage) are connected to another side of the CU. Every CC has input and output. Its input should be connected to the A vertical while its output should be connected to the B vertical of the crossbar selector. An input of the register should be connected to any available vertical of the crossbar selector.

First of all, subscriber A should pick up the handset in order to call subscriber

B. Picking up the handset results in closure of a subscriber loop. This closure makes a line relay (L) of the CU operate (check the appendix for detailed description of some

TE’s circuits operation). The L relay transmits received signal of connection request to the controller. The controller identifies the number of subscriber line.

The controller operates in a mode of register search then. Purpose of the register search is to select available register and connect it to the line of subscriber A.

If there are no registers available then the controller returns to initial state and subscriber receives the busy tone (f = 425 Hz, periodicity 1/3 s) from the CU.

Connection of the register is performed by the controller. The controller switches on a selecting electromagnet (SE) (its number assigned to the number of subscriber A) of the crossbar selector. Afterwards the controller switches on a hold up electromagnet (HE) of the vertical assigned to the register. Thus a switching point is created inside the crossbar selector. The switching point ensures connection of subscriber A to the register. The register sends the dial tone (f = 425 Hz) to subscriber

A then.

Hearing the dial tone subscriber A dials one-digit number of subscriber B. A telephone set transmits the number encoded in the decade code of loop pulses to the counter (shown in the figure 2). The counter counts the pulses. Information (in the multi-wires code) about the dialed digit goes through the decoder (a contact pyramid) to the digit clamper of the controller. The digit clamper stores the dialed digit.

Further the controller operates in the mode of automatic pre-hunting. In this mode the controller selects first available CC with the help of CC testing. If both CCs are busy then register resets to its initial state and subscriber receives the busy tone from the CU.

The controller perform directed line search if there is a CC available. This means the controller must determine the electromagnets of the crossbar selector (CS) in order to connect output of the CC to the line of subscriber B.

When the SE and HE are switched on the output of the CC should be connected to the CU of subscriber B in order to test a state of the CU (engaged or not). If subscriber B is talking (CU is engaged) then the CU (of subscriber A), controller and register are reset to initial state and subscriber A receives the busy tone from his CU.

17

Figure 2 – Block diagram of the controller

If subscriber B is not busy then the controller switches on the electromagnets of the CS in order to connect the input of the CC to the CU of subscriber A. After that the controller and register are reset to the initial state and the HE of the register’s vertical releases. The cord circuit itself ensures the operation of HEs of the input and output of the CC. The CC sends the ringing signal (f = 25 Hz) towards subscriber B and ringing tone (f = 425 Hz) towards subscriber A. Periodicity of sending is 1 second sending, 4 seconds pause.

Subscriber B must pick up the handset in order to answer a call. The answer

(closure of subscriber loop) is detected by CC. The signals of ringing and ringing tones are sent no more. The CC creates voice circuit and power circuits for the microphones for subscribers’ phones.

The CC performs the supervision of subscriber lines. If one of subscribers puts the handset down (generates on-hook signal) then the HEs are switched off, switching point inside the CS is destroyed and another subscriber receives the busy tone from his CU.

The given above process of connection between two subscribers can be visualized with the help of time chart given in the figure 3.

Closed loop of subscriber lines is marked with thick lines.

Figure 3 – Steps of connection establishment

18

1 Subscriber A requests connection. The register should be connected and subscriber

2 Dialing.

3 Connection establishment through the CC (if subscriber B isn’t busy).

4 Sending the ringing signal and ringing tone.

5 Subscriber B answers and conversation happens.

6 Subscriber A puts his handset down (on-hook).

7 Subscriber B puts his handset down (on-hook).

## 3 Test questions

3.1 How do you understand the term of connection request?

3.2 What is difference between automatic and directed search?

3.3 Why is it necessary to connect the output of the CC to the CU-B at first?

3.4 Why do we need the ringing tone? What is difference between the ringing tone and the busy tone?

3.5 Name the main functions of the CC.

3.6 How does subscriber B answer a call? What is on-hook signal?

3.7 Name the main functions of the controller.

3.8 Name all the cases when subscriber A can receive the busy tone.

4.1 Use the methodical instructions and appendix to learn the construction and operation principles of the crossbar exchange of low capacity.

4.2 Use the figure 1 (a) to draw the connecting path between subscriber A and subscriber B.

4.3 Answer the test questions in writing. Use the table 1 to draw some necessary circuits.

Answer two questions and draw two circuits according the table below.

№ of your team in subgroup

Draw the following electric circuits

1

2

3

4

3.1, 3.5

3.2, 3.6

3.3, 3.7

3.4, 3.8

A4, A5

A3, A5

A2, A5

A1, A5

## 5 Research plan

5.1 Familiarize yourself with the panels 2 and 3 of a laboratory stand.

5.2 Connect three phones to the three CUs (shown on the panel 2) according to your variant from the table 2.

19

5.3 Use three-wire cords to connect three CUs to horizontals while the CC1,

CC2 and the register should be connected to the verticals of the crossbar selector

(5×10×6). Perform all connections according the variant from the table 2.

Table 2 – Options of connecting CUs and other devices.

№ of your team in subgroup

№ of horizontals inside the CS

CU-1 CU-2 CU-3

CC-1 input

№ of verticals inside the CS

CC-2 output input output

Register

1

2

3

4

1

4

7

10

2

5

8

1

3

6

9

5

1

5

4

3

2

3

5

4

3

2

1

5

4

1

2

1

5

4

3

2

5.4 Use the methodical instructions and figure 3 to establish connection between two phones. You operate the controller. During that pay your attention to operation of the CS, CU LED signalization, operation of SEs and HEs, creation of switching points and subscriber information.

5.5 The subscribers’ numbers, numbers of SEs and HEs involved in your connection should be marked at the connecting path.

5.6 Establish connection between two subscribers. Keep it intact and try to dial a number of one of the subscribers using the third phone. Explain what happens then.

## 6 Report contents

6.1 Answers to the test questions and diagrams of electric circuits according to

4.3 and table 1.

6.2 The diagram of connecting path according to 4.2 containing the subscribers’ numbers, numbers of SEs and HEs involved in your connection.

20

Basic information about schematics of the crossbar TE

A1 Arbitrary signs

## APPENDIX

windings, anchors are released).

All the contacts of all circuits are shown unclosed (no current through

If a relay triggers you should imaginary move the contacts to the operation position.

Possible ways of imaging:

(a)

simplified method; (b) coordinate method; (c) symbolic method.

21

A2 Construction principles of electric circuits

The customer units and cord circuits of the TE of low capacity are pretty similar to the CU and CC of the K-50/200 crossbar TE. Requesting connection, subscriber accesses the register first, which is similar to K-50/200. After dialing the controller selects any available CC and connects subscriber lines by switching on the electromagnets of CS.

Let’s look closer at some circuits involved in TE operation.

A2.1 Customer unit operation

Every CU has two relays: the L relay and R relay. The L relay detects connection requests (from a subscriber) while the R relay ensures switching of the register and CC.

A simplified circuit of the CU is shown in the figure A1. If the voice wires a and b are closed by the cradle switch (CS) then there is a current flow through the winding of the L relay. The L relay triggers (drags up its anchor) and connects the winding of the R relay to the c wire. With its other contact the L relay sends a signal to the controller. The controller ensures connection between the CU-A and register.

This circuit also shows how the busy tone is sent towards the off-hook subscriber. If one of the subscribers (for example subscriber B) puts his handset on the phone then the CC resets to its initial state. When the CC is being reset the L relay of subscriber A releases immediately while the R relay (operating slowly) is held up via the line of subscriber A. Subscriber A hears the busy tone then. Subscriber A should put his handset on the phone in order to release the R relay.

22

Figure A1 – The circuit of receiving the connection request signal and sending the busy tone for off-hook subscriber

A2.2 Dialing

Figure A2 shows the simplified circuit of dialing. The pulse relay A of the register operates through the closed line loop of subscriber A. The relay switches on the hold up relay U with its contact A2.

The U relay prepares the transmission circuit for dialing pulses towards the counter. During each break of the pulse spring of a dial pulser the A relay releases and uses its A1 contact to supply “+” (of a battery) to the counter. The U relay holds its anchor during the whole series of pulses. The figure A2 shows the dialing time chart as well.

A2.3 Testing engagement of the subscriber B line

The P relay of the CC tests whether the line of subscriber B is engaged.

To do the test the output of the CC must be connected to the CU of subscriber B with the help of the c wire. The P relay has two windings. The first one is low-ohmic (for example 60 Ohm) and the second one has far higher resistance (for example 1000

Ohm).

23

Figure A2 – Dialing

A simplified circuit of testing the CU of subscriber B is shown in the figure

A3. The P1 winding (60 Ohm) of the P relay of the first CC is connected via the c wire to the CU of subscriber B. The circuit of current closes through the windings of relays L and R of the CU-B. The windings are connected sequentially.

Figure A3 – Circuits of testing the CU-B

24

The parallel connection of the second CC to the CU-B creates parallel and sequential current circuits. The I

2

current of the P2 relay is insufficient to cause relay operation because the P2 relay is partly shunted by the low-ohmic winding of the P1 relay (already connected to the CU-B).

A 2.4 Sending ringing signal for subscriber B

If the output of the CC is connected to CU-B while its input is connected to the

CU-A then subscriber B receives ringing signal and subscriber A receives the ringing tone (check A4).

Figure A4 – The circuit of: sending ringing signal, detecting the answer and microphone power supply

The relay of microphone power supply (for subscriber A) and additional relay

(VA) operate already. The winding of the PV relay connects to the generator of tone signals with the help of its VA contacts. The generator of alternating current (f = 25

Hz) uses its PV contacts to connect to the a wire of the CC (connection periodicity

1/4 s). Ringing current flows through the winding of the slowly operating relay (V), through the contacts of PV relay, through the P relay, through the “vertical-field” contacts of the CS and then through the CU and SL to the phone of subscriber B.

Inside the phone the current flows through the cradle switch, through the bell, through the capacitor (C) and finally returns via the b wire to the generator (f = 25

Hz) of TE.

The ringing current doesn’t cause operation of the V relay (it operates slowly).

At the same time the ringing tone is switched to the line of subscriber A with the help of contacts of the PV relay.

Subscriber B should pick up the handset to answer a call. It can happens either during ringing or during pause.

25

In the first case the V relay (it detects the answer) of the CC will be triggered by the direct current due to the closure of subscriber loop. The V relay switches on the additional winding of the B-200 relay. This relay interrupts the circuit of the PV relay which seizes up ringing. The hold up circuit for the B relay is created by the

500 ohmic line windings via the loop of subscriber B. The circuit ensures power supply for a microphone of the phone B (TS-B).

In the second case there is no current flow through the PV relay and the current flow through the line windings of the B relay is created immediately. Ringing signals are sent no more.

A 2.5 Speech transmission path

Diagram of the speech transmission path is shown in the figure A5. The microphones are powered separately through the windings of the relays A and B.

These relays operate during conversation and, thus, control the subscriber loop.

The CC provides power supply for the hold up electromagnets of the CS. In the figure A5 it is shown as the U relay (the hold up relay).

Figure A5 – Diagram of the speech transmission path

26

## VOCABULARY FOR THE LABORATORY LESSON

17

Alternating current – змінний струм

Automatic pre-hunting – вільний попередній пошук

Block diagram – структурна схема

Break and close – розмикати та замикати

Busy tone – сигнал «зайнято»

Channel – канал

Capacitor – конденсатор

Circuit – схема

Carbon powder microphone – вугільний мікрофон

Coil – катушка

Connection request – запит на з’єднання (виклик абонентом станції)

Сord circuit (CC) – шнуровий комплект

Сrossbar selector – багатократний координатний з’єднувач

Crossbar telephone exchange – координатна АТС

Customer unit (CU) – абонентський комплект

Decade code of loop pulses – декадний код шлейфні імпульси

Decoder – дешифратор

Dial pulser – номеронабирач

Dial tone – сигнал «відповідь станції»

Digit clamper – фіксатор цифр номеру

Direct current – постійний струм

Directed line search – вимушений лінійний пошук

Handset – слухавка (мікротелефонна)

Hold up electromagnet (HE) – утримуючий електромагніт

Keytone senders – кнопковий номеронабирач

Laboratory stand – лабораторний стенд

LED indicator – світлодіодний індикатор

Loop of subscriber line – шлейф абонентської лінії

Low-ohmic – низькоомний

Multi-wires code – багатопроводний код

Polarized magneto bell – поляризований дзвоник змінного струму

Pulse springs – імпульсні контакти

Register search – регістровий пошук

Relay – реле

Ringing signal – сигнал виклику

Ringing tone – сигнал КПВ

Ringing units – викличні прибори

Selecting electromagnet (SE) – вибираючий електромагніт

Series of pulses – серії імпульсів

Schematic diagram – принципова схема

Shunt springs – шунтуючі контакти

Speech transmission path – розмовний тракт

Stage of subscriber selection – ланка абонентського пошуку

Subscriber – абонент

Subscriber loop – абонентський шлейф

Switching point – точка комутації

Telephone exchange – телефонна станція

Tone ringer – пристрій тонального виклику

Transformer – трансформатор

Winding – обмотка

МІНІСТЕРСТВО ТРАНСПОРТУ ТА ЗВЯЗКУ УКРАЇНИ

ДЕРЖАВНИЙ ДЕПАРТАМЕНТ З ПИТАНЬ ЗВЯЗКУ ТА ІНФОРМАТИЗАЦІЇ

ОДЕСЬКА НАЦІОНАЛЬНА АКАДЕМІЯ ЗВ'ЯЗКУ ім. О.С. ПОПОВА

27

Кафедра комутаційних систем

М Е Т О Д И Ч Н І В К А З І В К И до виконання лабораторної роботи 18

КВАЗІЕЛЕКТРОННА АТС МАЛОЇ ЄМНОСТІ з курсу «Cистеми комутації електрозвязку»

M E T H O D I C A L I N S T R U C T I O N S for laboratory lesson

18

“QUASIELECTRONIC EXCHANGE

OF LOW CAPACITY” within the course of telecomminication switching systems

## Odessa 2008

28

Укладачі: Ложковський А.Г., Бабіч Ю.О.

29

## 1 Learning objectives

a) Learn the operation principles of a fereed and fereed switch. b) Learn construction and operation principles of the quasielectronic telephone exchange (QTE) of low capacity.

## 2 Theory

2.1 Block diagram of the QTE

The quasielectronic TE switches voice channels with the help of the fereeds

(contact elements). The fereeds are controlled by a controller. A simplified block diagram of the QTE is given in figure 1. Equipment of the QTE consists of two parts.

These parts are represented by the telephone periphery (TP) and the controllers.

Figure 1 – The simplified block diagram of the QTE

The TP is represented by the switch, register (R), input and output trunk terminations (ITT/OTT), cord circuit (CC).

The QTE has two controllers. The central controller (CeC) consists of two computers. Their software ensures connections of all types.

The peripheral controller (PC) ensures interaction between the CeC and peripheral equipment. It controls time and electric parameters of the signals transmitted between CeC and TP.

30

2.2 How the fereed works

The fereed is a switching element of the QTE. The fereed is a sealed contact with magnetic hold up provided by an external magnet with a rectangular hysteresis loop.

Figure 2 shows the fereed with one sealed contact working for closure. The fereed can have two or four glass flasks. Every flask contains two contact springs made of magnetic material. Ends of the contact springs are covered with precious metal in order to provide a reliable contact. The contacts are protected from moisture while the flask is filled up with inert gas in order to prevent sparking.

1

2

3

4 a b p x1 k k

Y2 p k x2 p p

Y1 k

+I k

+I

Y

(IW)

X1

(IW)

XC

(IW)

Y2

(IW)

X2

(IW)

Y1

(IW)

YC

## –

c

(IW)

X1

(IW)

X2

Figure 2 – How the fereed works

The fereed’s magnetic system includes the external core (3) with the rectangular hysteresis loop and contact springs.

The magnetic shunt (4) (the reflector) divides the magnetic system into two parts (check figure 2). It is made of soft magnetic material which reduces interaction of magnetic fields.

There are two windings (X and Y) winded around the core (3). They control breaking and closure of the contact springs. Every winding has two parts. Having 2W wraps the X

1

winding is winded to the left from the reflector while the X

2

winding

(with W wraps) can be found to the right of the reflector. These parts of the X

31 winding create oppositely directed magnetic fluxes. Parts of the Y winding are situated in the same way. The Y

1

(of 2W wraps) is on the left from the reflector whilst the Y

2

winding (of W wraps) is on the right.

A generator of bell-shaped pulses (GBP) must be connected to the control windings. It generate pulses with amplitude of 8,5 A lasting for 0,6 ms.

Current from the GBP should flow through the X and Y windings at the same time in order to close contacts. This creates four magnetic motion forces (MMF).

They are IW

(X1)

, IW

(Y1)

, IW

(X2)

and IW

(Y2)

. Total MMF of the left part equals:

IW

(Y)

= IW

(X1)

– IW

(Y2)

(see vector chart of the figure 2 b), whist the MMF of the right part is

IW

(Y)

= IW

(Y1)

– IW

(X2)

Opposite poles (S and N) appear at the ends of the contact springs due to the same direction of those total MMFs. As the result the springs are attracted to each other. The contacts are held up together due to residual magnetization. It takes only

1…2 ms to close the contacts.

Current from the GBP should flow through one of the windings (X or Y) in order to break the contact springs. The figure 2 (c) shows the vectors of MMF of current flowing through the X winding. The X

1

and X

2

create opposite MMF fluxes.

This results in appearance of similar poles (for example S and S) at the ends of the contact springs. The springs break then.

2.3 The fereed selector

The fereed selectors (FS) are based on the sealed contacts. The fereed selectors may have different quantity of inputs (n) and outputs (m). They can switch different numbers of wires. Every FS consists of a contact matrix and control matrix (check figure 3).

Figure 3 – Block diagram of the FS matrix

Figure 4 shows the diagram of the contact matrix whilst the figure 5 shows control matrix of the 4×4×1 FS (n×m×l).

32

The control matrix consists of the X and Y windings connected sequentially.

The fereeds assigned to the horizontals (H0…H3) and verticals (V0…V3) select the coordinates of a switching point. The fereeds are controlled by the controller. Current from the GBP should reach the X and Y windings (crossed at a switching point) simultaneously in order to close contacts of the switching point (In the figure 5 such places are marked with circles).

Figure 4 – The 4×4×1 contact matrix

Contacts of the switching point stay closed due to residual magnetization. It is necessary to provide pulse of current (form the GBP) for one of the windings in order to release the switching point. The figure 5 shows that it can be done if you select the

H3 horizontal and close the G relay and the reset relay. It is all done by the controller.

Commands from the controller are transmitted via the address busses (AB). Time chart of the fereed selector operation (which creates and releases the switching points) is given in the figure 6. If the GBP switches on in order to create the switching point then the switching points (already created at the same horizontal or vertical) will be released. Thus only one switching point can exist at the horizontal or vertical. However information about a state of the switching point is stored in special memory.

33

AB

Figure 5 – The 4×4×1 control matrix

H j

V j

Figure 6 – Time chart of the fereed selector operation

34

## 3 Test questions

3.1 What should be done in order to create the switching point?

3.2 What should be done in order to release the switching point?

3.3 How many fereeds are on during a conversation of two subscribers? Why do they stay closed?

3.4 Is it possible to create two switching points at the same horizontal of the fereed selector?

4.1 Use the methodical instructions (Figures 2 and 7) to learn: a) how the fereed selector works; b) construction of the QTE of low capacity and the process of connection establishment between two subscribers.

4.2 Answer the test questions in writing.

4.3 Draw the block diagram of the QTE (use figure 7 for it). Connect the CU, register and CC according to your home task variant (check the table 4.1).

Table 4.1 – Home task variants

Subscriber A

Team № Subscriber’s number

Horizontal

1

2

5

7

3

2

3

4

2

1

4

5

Subscriber B

Subscriber’s number

Horizontal

9

4

5

1

3

6

2

3

1

Verticals of the FS

2 3

Register CC input CC output

CC input Register CC output

CC output CC input Register

Register CC output CC input

4.4 Draw the control matrix of the given TE. Mark the current path required for creation of the switching point with coordinates of H2V3.

QTE.

4.5 Draw the connection path for two subscribers (A and B) connected by the

## 5 Research plan

5.1 Familiarize yourself with the FS and its controller console.

Switch on the switching points listed below.

switch on the SP № 10;

switch on the SP № 22;

switch on the SP № 24, check out the SP №22;

switch on the SP № 77.

Turn the power off. Turn the power on again. What have happened to the

SPs?

switch on the SP № 10;

switch on the SP № 24;

35

switch on the SP № 07, what happens to the SP №77?

switch off the SP № 07.

Shortly write down your observation results.

5.2 Use 6.2 to get familiar with the panels of the laboratory stand where the circuits of the QTE can be found.

5.3 Use three-wired cords in order to perform connection according to your task variant (check the table 4.1).

– Connect the subscriber units to the FS horizontals;

connect the register and CC to the FS verticals.

Use the face program panel of the controller console in order to program numbers of the subscribers (A and B) according to the table 4.1.

Connect phones to the inputs of the CCs.

5.4 Use Chapter 7 to perform connection between the subscribers.

Pay your attention at the information signals for subscriber A and at the visual indication of the TE’s devices operation.

Pay your attention at the information signals for subscriber B and at the visual indication of the TE’s devices operation.

5.5 Describe the steps of connection establishment shortly.

## 6 Laboratory equipment

6.1 The laboratory stand of the FS

Portable laboratory stand contains typical 8×8×2 FS. It has two sections with n

= 4 and m = 8 each.

The matrix of voice contacts is shown at the blue background of the laboratory stand’s face panel. The 07-th, 10-th, 24-th and 77-th SPs are equipped with the light emitting diodes in order to let you watch breaking and closure of the contacts.

The control matrix is divided into two sections (C0 and C1).

Every switching point has definite address consisting of the horizontal coordinate (H0, H1, H2, H3) and vertical coordinate (V0,V1…V7). There are additional coordinates C0 and C1 for section selection. Use appropriate toggle switches (situated at the diagram of the controller) to select coordinates of the switching points. Press the button to switch the GBP on.

Take the following steps in order to release SP:

select the section;

select the horizontal;

switch on the “Release” toggle switch;

press the button to switch the GBP on.

36

6.2 The laboratory stand of the QTE

Figure 7 – Functional diagram of the QTE of low capacity

Laboratory stand (panels 2 and 3) contains a model of the QTE handling 5 numbers (figure 7). It has following equipment:

five customer units (CU) (only three are shown);

one cord circuit;

one 5×3 FS;

the register (R) and controller (this QTE doesn’t contain peripheral controller).

Every subscriber line is switched to its CU. Every CU is switched to one of the horizontals (horizontal buses of the FS).

The register, input and output of the CC must be connected to the three vertical buses (verticals) according to your variant.

You can find the control matrix to the left of the FS contact matrix. The control matrix depicts contacts of the V and H relays (they create switching point).

## 7 Connection

CU identifies connection request from the subscriber A. The controller

(scanning the CUs) perceives the request. The controller determines a number of the

CU and tests register. If the register is idle then controller switches on the V and H relays (creates a switching point). This switching point ensures connection between subscriber A and the register.

You can do this in the lab by pressing necessary V and H buttons simultaneously. The fereed situated at the intersection of the V bus and H bus will be magnetized due to a pulse from the GBP.

Subscriber receives the dial tone from the register. Subscriber A dials one-digit number of subscriber B. The counter of the register receives series of pulses and transmit them through the decoder to the controller (it is shown in the figure 8). This

37 information is transmitted through the socket panel (used for programming subscriber numbers) to one of the control relays (it is assigned to the horizontal where subscriber

B is connected to). Use wire with plugs in order to assign one-digit number to any

CU (of 5 accessible) at this panel. For example you can assign number “8” to the fifth horizontal.

After receiving a number of subscriber B the controller selects the CC. If the

CC is occupied then the controller resets the register and subscriber A receives a busy tone from his CU.

If the CC is idle then the controller connects output of the CC to the CU of subscriber B. To perform such connection it is necessary to create the switching point at the intersection of the necessary horizontal and the vertical where the output of CC is connected to.

After creation of the switching point the CC tests the CU of subscriber B. If the

CU of subscriber B is occupied then the CU, controller and register are reset to initial state whist subscriber A receives the busy tone from his CU.

Figure 8 – Panel for programming subscribers numbers

If subscriber B is not busy then the controllers continue switching. It connects input of the CC to the line of subscriber A by creating the switching point.

It is necessary to reset the register to initial state then. It is done by switching on the release relay (R) and the V relay of the vertical where the register is connected to. In this case current flows only through one winding of the SP.

The switching point will be destroyed due to remagnetization of the fereed.

The CC sends a ringing signal to the line of subscriber B and ringing tone towards subscriber A.

Subscriber B should pick up his handset to answer a call. The CC identifies answer of subscriber B and stops sending the ringing signal and ringing tone. It

38 creates voice transmission path then. The CC provides power supply for both microphones and performs supervision of subscriber lines.

If one of the subscribers puts his handset on the phone then the CC resets to its initial state. Thus the controller must create a circuit for the V relay (of appropriate verticals of the CC) and it must switch on the R relay.

## 8 Report contents

8.1 Your SP observation results (according to 5.1).

8.2 Answers to the test questions.

8.3 The control matrix of the QTE according to 4.4.

8.4 Voice transmission path for two subscribers of QTE (including switching points inside the FS) according your variant from the table 4.1. A list of steps for connection.

## VOCABULARY FOR THE LABORATORY LESSON

18

Alternating current – змінний струм

Block diagram – структурна схема

Break and close – розмикати та замикати

Busy tone – сигнал «зайнято»

Channel – канал

Circuit – схема

Carbon powder microphone – вугільний мікрофон

Central controller – центральний керувальний пристрій

Connection request – запит на з’єднання (виклик абонентом станції)

Сord circuit (CC) – шнуровий комплект

Customer unit (CU) – абонентський комплект

Decade code of loop pulses – декадний код шлейфні імпульси

Decoder – дешифратор

Dial pulser – номеронабирач

Dial tone – сигнал «відповідь станції»

Direct current – постійний струм

External core – зовнішнє осердя

Fereed – ферит

Fereed selector (FS) – багатократний феридовий з’єднувач

Generator of bell-shaped pulses (GBP) – генератор дзвоноподібних імпульсів

(ГДІ)

Handset – слухавка (мікротелефонна)

Quasielectronic telephone exchange (QTE) of low capacity – квазіелектронна автоматична телефонна станція (АТСКЕ) малої ємності

Input and output trunk terminations – вхідні та вихідні лінійні комплекти

Laboratory stand – лабораторний стенд

Loop of subscriber line – шлейф абонентської лінії

Peripheral controller – периферійний керувальний пристрій

Relay – реле

Ringing signal – сигнал виклику

Ringing tone – сигнал КПВ

Sealed contact – герметичний контакт

Series of pulses – серії імпульсів

Schematic diagram – принципова схема

Speech transmission path – розмовний тракт

Subscriber – абонент

Subscriber loop – абонентський шлейф

Switching point – точка комутації

Telephone exchange – телефонна станція

Telephone periphery – телефонна периферія

Winding – обмотка

39

40

## References

1. Автоматическая коммутация: Учебник для вузов / О.Н. Іванова, М.Ф. Копп,

З.С. Коханова, Г.Б. Метельский; Под ред. О.Н. Ивановой. – 2-е изд. доп. и перераб. – М.: Радио и связь, 1988.

2. Станционные сооружения городских телефонных сетей: Учебник для рабочих связи; Под ред. Ю.Н. Корнышева. – М.: Радио и связь, 1987.

3. Телефонні апарати: Метод. керівництво до лаб. роботи №11 за курсом

«Системи комутації в електрозв'язку» / Укл. А.Я. Маркович, Г.В. Стовбун.

Одеса, ВЦ ОНАЗ, 2002.

4. Методичні вказівки до лабораторної роботи № 17 “Координатна АТС малої ємності” /Укл. В. М. Романцов. Одеса, ВЦ ОНАЗ, 2002.

5. Квазіелектронна АТС малої ємності: Метод. указівки до лаб. роботи №18 з курсу “Системи комутації в електрозв'язку” / Укл. В.М. Романцов. Одеса, ВЦ

ОНАЗ, 2001.